[lammps-users] Correct utilizatioon of Fix Move Command

Dear Lammps Users, I am working on a 2D framework which should be submitted to a unidirectional strain, in order to evaluate some elastic properties.

I think I may use the Fix Move command by “pinning” a few rows of atoms at the extreme opposite ends of the monolayer and submitting them to the movement imposed by fix move.

I read that “The atoms affected by this fix should not normally be time integrated by other fixes (e.g. fix nve, fix nvt), since that will change their positions and velocities twice”. so I put the fix move and the definition of groups of atoms to be moved before fix nve instruction.

Is this an appropriate way to manage this isssue?

Herebelow please find the input script.

I would like to avoid stupid mistakes before moving to larger frameworks, so any comment and/or recommendation will be very welcome.

Paolo Botto

MONOMERIC UNITS E 40 X 40 FRAMEWORK filename in-E40-00

obviously not.

Hi Paolo,

If I interpret the message “The atoms affected by this fix (…)” correctly, you should apply the fix nve ONLY to the atoms that ARE NOT already in groups “up” and “down”.



Hi Simon, thanks for your kind answer and for your patience. You are right.

Reading more carefully the “group” command documentation, I think the correct approach is to make use of something like:

“group PIPPO subtract all UP DOWN”; this collects in PIPPO all the atoms not belonging to UP or DOWN,

and then:

fix nynve PIPPO etc.

I should be more careful in studying the documentation before asking silly questions

my apologies


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